[libcamera-devel] [PATCH v4 25/32] ipa: rkisp1: awb: Use frame context to fix gains calculations

[Jacopo Mondi]

Hi Laurent

On Thu, Sep 08, 2022 at 04:41:53AM +0300, Laurent Pinchart via libcamera-devel wrote:
> The AWB statistics are computed after the ISP applies the colour gains.
> This means that the red, green and blue means do not match the data
> coming directly from the sensor, but are multiplied by the colour gains
> that were used for the frame on which the statistics have been computed.
> The AWB algorithm needs to take this into account when calculating the
> colour gains for the next frame. Do so by dividing the means by the
> gains that were applied to the frame, retrieved from the frame context.
>
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

Good catch!

Reviewed-by: Jacopo Mondi <jacopo at jmondi.org>

Thanks
  j

> ---
>  src/ipa/rkisp1/algorithms/awb.cpp | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/src/ipa/rkisp1/algorithms/awb.cpp b/src/ipa/rkisp1/algorithms/awb.cpp
> index bb0f6c27fc7d..b711e93b73ba 100644
> --- a/src/ipa/rkisp1/algorithms/awb.cpp
> +++ b/src/ipa/rkisp1/algorithms/awb.cpp
> @@ -207,6 +207,15 @@ void Awb::process(IPAContext &context,
>  	double greenMean = 1.1636 * yMean - 0.4045 * cbMean - 0.7949 * crMean;
>  	double blueMean = 1.1636 * yMean + 1.9912 * cbMean - 0.0250 * crMean;
>
> +	/*
> +	 * The ISP computes the AWB means after applying the colour gains,
> +	 * divide by the gains that were used to get the raw means from the
> +	 * sensor.
> +	 */
> +	redMean /= frameContext.awb.gains.red;
> +	greenMean /= frameContext.awb.gains.green;
> +	blueMean /= frameContext.awb.gains.blue;
> +
>  	frameContext.awb.temperatureK = estimateCCT(redMean, greenMean, blueMean);
>
>  	/* Estimate the red and blue gains to apply in a grey world. */
> --
> Regards,
>
> Laurent Pinchart
>